The present invention relates to a liquid crystal display device, and particularly to a liquid crystal display device which includes a plurality of liquid crystal layers lying in piles, and in which special attention is paid to the generation of a white on black pattern based upon an overlap of patterns formed respectively in the liquid crystal layers, that is, the generation of the above-mentioned white pattern is prevented or positively utilized.
According to one aspect of the present invention, a liquid crystal display device is proposed in which the generation of white on black patterns is prevented.
In an electronic device having a display part such as a wrist watch, a small-sized clock, or an electronic desk calculator, a liquid crystal display device has been widely used as the above display part in recent years. Further, there has been developed a watch or clock in which, as shown in FIG. 1 of the accompanying drawings, a display part 1 is divided into an analog display region 5 having short, long and second hands 2, 3 and 4 and a digital display region 6 for indiating the time by numerals. The display part 1 may be fabricated in such a manner that the analog and digital display regions 5 and 6 are formed of liquid crystal layers 7 and 8 respectively, as shown in FIG. 2. In more detail, the upper and lower liquid crystal layers 7 and 8 include therein analog and digital display patterns respectively. Further, upper and lower polarizers 9 and 10 are arranged above and below the liquid crystal layers 7 and 8 respectively, and a reflecting plate 11 is arranged below the lower polarizer 10. The polarizers 9 and 10 are equal in direction of transmission axis to each other.
In such a two-layer structure, when a portion (or a segment) of the upper liquid crystal layer 7 and a portion (or a segment) of the lower liquid crystal layer 8 overlap each other and moreover are simultaneously applied with a voltage, an overlapping portion of the segments forms a white on black pattern on a display surface. For this reason, the display part 1 is so designed that respective patterns in the liquid crystal layers 7 and 8 are prevented from overlapping each other. That is, the display part 1 is obliged to become large, and therefore it is impossible to provide a small-sized electronic device.
Now, explanation will be made in detail on the phenomenon that, in a case where respective segments of upper and lower liquid crystal layers overlap each other and are simultaneously applied with a voltage, an overlapping portion of the segments forms a white on black portion on a display surface and cannot be observed visually, by reference to FIGS. 3a and 3b. FIG. 3a is an exploded, explanatory view for showing a display part including liquid crystal layers and polarizers. Referring to FIG. 3a, an upper polarizer 12, a glass plate 13, an upper liquid crystal layer 14, a glass plate 15, a glass plate 16, a lower liquid crystal layer 17, a glass plate 18 and a lower polarizer 19 are arranged in the order described in the direction from top to bottom. In FIG. 3a, reference characters a, b, c and d designate points where light passes through the display part. In more detail, light passes through the upper polarizer 12, the upper liquid crystal layer 14, the lower liquid crystal layer 17 and the lower polarizer 19 at the points a, b, c and d respectively. Further, reference numberals 1 , 2 and 3 designate paths of light travelling in a direction from top to bottom, and 1 ', 2 ' and 3 ' those of light travelling in a direction from bottom to top (usually, the paths of light reflected back from a reflecting plate). Referring to FIG. 3a, on the paths 1 and 1 ', there is provided no electrode for the liquid crystal layers 14 and 17. On the paths 2 and 2 ', there are provided a pair of electrodes 20 which are formed on the glass plates 13 and 15 for sealing up the upper liquid crystal layer 14 therebetween. On the paths 3 and 3 ', there are provided upper electrodes 20 for the upper liquid crystal layer 14 and lower electrodes 20 for the lower liquid crystal layer 17. That is, the upper electrodes 20 and the lower electrodes 20 overlap each other.
FIG. 3b shows the polarization direction of light at a time immediately after light has passed through the members 12, 14, 17 and 19. In FIG. 3b, reference symbols .rarw..fwdarw. and designate polarization directions of polarized light, and x shows that light has been absorbed and therefore a pattern becomes black on a display surface. The polarization direction of light is not changed when the light passes through that portion (or segment) of a liquid crystal layer which is applied with a voltage, but is changed by an angle of 90.degree. when the light passes through a segment which is not applied with any voltage. Accordingly, in a case where light travels along the paths 1 and 1 ', on which the upper and lower liquid crystal layers 14 and 17 are not applied with any voltage, light passes through the upper polarizer 12, the liquid crystal layers 14 and 17 and the lower polarizer 19, and therefore no pattern appears on the display surface. In a case where light travels along the paths 2 and 2 ', on which only the upper liquid crystal layer 14 is applied with a voltage, the light travelling in the direction of the path 2 cannot pass through the lower polarizer 19 and therefore a black pattern is formed on the display surface, and the light travelling in the direction of the path 2 ' cannot pass through the upper polarizer 12 and therefore a black pattern appears on the display surface.
In a case where light travels along the paths 3 and 3 ', on which each of the upper and lower liquid crystal layers 14 and 17 is provided with a pair of electrodes 20, and where a voltage is applied across the layer 14 and across the layer 17 simultaneously, light passes through the members 12, 13, 14, 15, 16, 17, 18 and 19 and therefore forms a light region on the display surface. In other words, an overlapping portion of the electrode pair 20 for the layer 14 and that for the layer 17 forms a white on black region on the display surface when these electrode pairs are simultaneously applied with a voltage.
Accordingly, an object of the present invention is to provide a liquid crystal display device in which a plurality of liquid crystal layers are piled up to display several kinds of patterns on a display surface, and in which the generation of a white on black region based upon an overlap of the patterns is prevented to reduce the area of the display surface.
In order to attain the above object, according to an aspect of the present invention, there is provided a liquid crystal display device including a plurality of liquid crystal layers lying in piles, wherein polarizers are arranged between adjacent liquid crystal layers, above an uppermost liquid crystal layer, and below a lowermost liquid crystal layer, and adjacent polarizers are different in direction of transmission axis from each other.
Further, according to an application of the present invention, there is proposed a liquid crystal display device in which a white on black portion caused by an overlap of segments in liquid crystal layers is positively utilized as a display pattern.
In ordinary liquid crystal display devices, when a voltage is applied across a liquid crystal layer through electrodes for forming a predetermined pattern, the light having passed through that portion of the liquid crystal layer which is applied with the voltage and corresponds to the predetermined pattern, is different in polarization direction from the light incident upon the portion and therefore cannot pass through a polarizer. That is, the light having passed through the portion of the liquid crystal layer corresponding to the predetermined pattern forms a black pattern on a display surface. According to the above-mentioned method, it is difficult to obtain a colored display pattern, a display surface is not colorful nor fashionable, and moreover the design of display is subjected to a restriction. For example, in a case where a wrist watch 101 shown in FIG. 7 has a front face 103 which is black painted, it is required to provide a white window (or portion) 104 in a central part of the face 103 since numerals 102 for indicating the hour and the minute are displayed in black. Accordingly, restrictions are placed to the color and design of the wrist watch.
In order to solve the above difficulties, it has been proposed to color other portions of the front face 103 than a display pattern in order to make the wrist watch colorful. According to such a proposal, however, the colored portions are observed more clearly than the display pattern, which makes it difficult to read the display pattern. Thus, the wrist watch becomes inferior in display characteristic. In a case where the front face is colored in a quiet tint taking the above difficulties into consideration, the wrist watch becomes unfashionable.
In order to solve such problems, a display device (or a watch) is disclosed in a Japanese Patent Application which is now laid open under the number of 79663/79. In the above display device, a plurality of liquid crystal layers each containing one of various dichroic dyes for forming different colors are piled up to independently display respective patterns. That is. a pattern colored in a tint is formed by a liquid crystal layer, another pattern colored in another tint is formed by another liquid crystal layer, and so on. Thus, at least two kinds of colored patterns can be displayed. In such a structure, however, it is required to employ a plurality of expensive liquid crystal materials assuming different colors, and therefore the display device becomes expensive. Moreover, when patterns colored in different tints overlap each other, an overlapping portion is changed in color through the substractive mixture of color, and there arise problems in designing such as the unbalance of color.
Accordingly, as one application of the present invention a liquid crystal device is considered which employs a structural arrangement of conventional liquid crystal display devices to display a pattern by a white on black portion or by a colored portion corresponding to the white on black portion, and which is therefore inexpensive and fashionable.
Further, this application of the present invention is intended to provide electronic devices such as an electronic watch and an electronic desk calculator in which the above-mentioned liquid crystal display device is incorporated.
In this application of the present invention, there is provided a liquid crystal display device in which a plurality of liquid crystal layers each for forming a pattern are piled up, a pair of polarizers are arranged above and below the liquid crystal layers, and the patterns formed by the liquid crystal layers are arranged in such a manner that an overlapping portion of the patterns forms a desired display pattern. Further, in the above-mentioned liquid crystal display device, the light passing through the liquid crystal layers in the direction from bottom to top, namely, the light from a reflecting plate (or a light source) which is placed below the liquid crystal layers, is made to be a colored light to form the desired display pattern of a color. Furthermore, in the same liquid crystal display device, at least one of the liquid crystal layers contains therein a dichroic dye for forming a color to form the desired display pattern of the color.